2.5 Data analysis
We used linear mixed-effect models to test for the effects of warming
and N addition on plant dominance, flowering phenology and soil
characteristics. We treated warming, N treatment, species and year as
fixed factors, and the six blocks as random factors. P< 0.05 and P < 0.001 were used to indicate
significance and strong significance. First Optimization software
(7D-Soft High Technology Inc.) was used to fit the phenological
equation. Structural equation modeling (SEM) was used to study the
direct and indirect effects of temperature and nitrogen addition on
dominance of different species. SEM analysis was performed by AMOS 21.0
(AMOS Development Co.). We employed chi-square (χ2), P value, the
root means square error of approximation, normed fit index, incremental
fit index and Akaike information criterion to evaluate the goodness of
fit of the model. Other statistical analyses were performed in R4.2.2.